The purpose of this study was to identify early behavioral, physical and familial characteristics of children with a significant discrepancy between intellectual ability and school achievement. Low achievers, followed from the prenatal period to age 7, were compared with their IQ-matched academically successful controls on prospectively ascertained indices of cognitive and physical development and family environment. Cognitive deficits and behavioral deviations in the preschool period were associated with low achievement at age 7. Socio-economic status (SES) and family structure were better predictors of low achievement than were indices of physical development or medical status. Low achievers were born into low SES, large families and were primarily male. As preschoolers, they had difficulties with verbal tasks and relatively low IQ scores. At ate 7, signs of deviant behavior, verbal and non-verbal cognitive deficits, and neurological soft signs were present. Hyperactive low achievers had an increased frequency of obstetrical complications.